The invention described and claimed herein pertains generally to apparatus which is located aboard a platform in an acoustic environment, such as a water environment, for tracking a moving body when the body is very close to the platform. More particularly, the invention pertains to apparatus located aboard a vessel for enabling the vessel to monitor the course, performance and point of impact of a torpedo or the like, which is directed at the vessel for testing or other purposes. Even more particularly, the invention pertains to apparatus of the above type wherein information related to torpedo operation is obtained by distributing a number of discrete hydrophone elements around the hull of the vessel, and comparing the strength and arrival time at different hydrophones of acoustic information which is emitted by the body or generated by the impact of the torpedo against the vessel.
In the development of a torpedo system, it is necessary to periodically test the system by directing a torpedo toward a target vessel, either a submarine or a surface vessel, and to obtain various kinds of data during the course of torpedo operation. Desired information can include the attack or aspect angle of a torpedo, i.e., its bearing as it approaches a target vessel, and the location on the target vessel at which the torpedo strikes or impacts. Knowledge of the impact point may be very useful for developing torpedo evasion tactics, as well as for refining a torpedo guidance system. Other useful or vital information includes knowledge of whether a torpedo struck its target on its first pass, or missed, turned and reattacked. If the torpedo missed, it could be important to determine whether the torpedo went over or under the target, if the target vessel was a submarine. If the torpedo missed and did not return, it could be very important to be able to determine its bearing as it passed the target vessel, in order to recover the torpedo.
A torpedo on a test run sometimes carries an internal recorder, which provides considerable information relative to its own performance if the recorder is recovered. However, it very frequently happens that when the torpedo impacts a target vessel, the recording unit is unrecoverable. All data pertaining to torpedo operation while the torpedo is in close proximity to the target is thereby lost. Even if the recording unit is recovered, there is presently no way to determine therefrom the location of impact on the target vessel. Present techniques to determine impact location are limited to asking personnel stationed at different locations on the target vessel for their respective opinions as to the point where impact occurred. Such procedure has generally been of little or no value.
The sonar system located aboard a target vessel may have some utility in tracking a distant torpedo, but has been found to be of little help in locating a torpedo impact point, or in otherwise monitoring torpedo performance close to the target vessel.
By employing the present invention, data can be generated and recorded, and then analyzed under controlled laboratory conditions, to resolve questions pertaining to attack or aspect angle and impact location. Other information which can be provided by the invention includes the history of successive active sequences of torpedo operation, closing speeds of the torpedo relative to the target, torpedo miss and reattack performance, and successive torpedo motor speed changes. The invention also enables an operator aboard the target vessel to readily approximate both aspect angle and impact location, to within several feet, right after impact occurs.